The present invention relates generally to electronic circuits, and more particularly to electronic circuits with adjustable delay time for turning on or off an application device or an electronic load. Such circuits may be used in overload protection applications.
In a typical overload protection circuit, a resettable fuse, e.g., a positive temperature coefficient (PTC) device, is used. When there is a change in condition, such as occurrence of an overload, the PTC device trips and becomes a very large resistance, thus limiting the current flow and providing overload protection. When the new condition disappears, the resistance of PTC device decreases to its normal value, i.e., a low resistance value, and the application circuit resumes its normal operation.
In many instances, it may desirable to provide a delay time in turning off or on an application device or an electronic load. It may further be desirable to provide an adjustable delay, time upon a change in condition, such as occurrence of an overload or overheat. Also, fault conditions may occur when an electric motor is stalled or an electronic load is short circuited by accident. Such a condition change may also be intentionally generated as input signal to provide a longer delay time in turning off or on an application device or an electronic load.